1. Field of the Invention
The present invention relates to a measurement system and an interferometer.
2. Description of the Related Art
As a means for measuring the motion error of an industrial machine such as a three-dimensional measuring machine, a working machine (i.e., machine tool), and the like, a measurement system that moves a movable body (i.e., movement member) through the operation of the industrial machine and measures a coordinate value of the movable body by means of an interferometer is known in the art. A measurement sensor that is used for measuring a target object or a machining head device that is used for machining the target object is mounted on the movable body. For example, a tracking-type laser interferometer is used as such an interferometer for measuring the coordinate value of the movable body. An example of the tracking-type laser interferometer is disclosed in Japanese Unexamined Patent Application Publication No. 2008-128899. The tracking-type laser interferometer controls the emission direction of a beam of laser light to keep track of a retro reflector that is attached to the movable body. In addition, the tracking-type laser interferometer utilizes laser interference to measure a distance therefrom to the retro reflector. A plurality of such tracking-type laser interferometers is provided inside the measurement space or the machining space of the industrial machine. For example, three tracking-type laser interferometers are provided inside the space. Each interferometer keeps track of the retro reflector and measures a distance therefrom to the retro reflector. The measured distance from each interferometer to the retro reflector is used for trilateration. By this means, it is possible to find a three-dimensional coordinate value of the retro reflector, that is, a three-dimensional coordinate value of the movable body.
However, when a tracking-type laser interferometer is used for measuring a three-dimensional coordinate value of a movable body, it is necessary to install the tracking-type laser interferometer inside the measurement space or the machining space of an industrial machine. For this reason, there is a risk that the movable body moves too close to the interferometer and collides with the interferometer in a case where a defective movement program designed for moving the movable body is inputted in the industrial machine. There is the same risk as above in a case where, when an operator manually operates the industrial machine to move the movable body, the operator fails to operate the industrial machine properly. The same holds true in a case where an operator fails to install the interferometer at a proper installation position.